In internal combustion engines, it is essential that the cylinders be sealed completely airtight when the valves are closed to ensure efficient fuel consumption and transfer of power. This airtightness is achieved, among other things, by assuring that the valve heads perfectly match the valve seats. Since contact surfaces of the valves and valve seats are subject to wear and other degrading factors that effect the contact surface textures, these surfaces must be modified to re-establish the high quality seal.
It is well known among vehicle mechanics that valve seats can be machined to remove the outer surface of the seat to expose a smooth and uniform contact surface by a technique commonly referred to as xe2x80x9clappingxe2x80x9d. This lapping technique is accomplished by removing the cylinder head from the engine and machining the valve seats with a cutting blade. Typically, a valve seat has a profile with three different angles: a throat angle, a valve seat angle, and a top angle. Thus, a xe2x80x9cthree-anglexe2x80x9d cutting blade or bit is used to machine a valve seat wherein each angle of the three-angle cutting blade corresponds to one of the valve seat angles to be machined. Three-angle cutting blades vary in size and shape depending on the type of cylinder head valve seat being machined. These three-angle cutting blades are currently used by all current valve seat and guide manufacturers including Berco, AZ, AMC, Vereco, Mira, Peterson, Robbi, Kwik-Way, DCM, Kansas Instruments, Sunnen, Serdi, NEWEN, TandS, Winona Van Norman, etc.
A disadvantage of the lapping technique is the risk of damage to the surface finish from vibrations, chattering, or undulations generated from flexion of the cutting bits. This problem develops because certain large-diameter cylinder head valve seat shapes require a three-angle cutting blade with a long cutting edge/surface. Cutting efforts with this long cutting edge/surface create flexions at the level of the spindle of the cutting or on the cylinder head, especially when dealing with valve seat material that is difficult to machine. These flexions generate vibrations, chattering, or undulations which, in turn, damage the surface finish of the valve seat making the quality of the work unacceptable by OEM (original equipment manufacturer) standards.
Another disadvantage of the lapping technique is a de-centering phenomena. As stated above, cutting efforts with a long cutting edge/surface create flexions. These flexions create an unbalanced radial cutting effort which de-centers the three-angle cutting blade.
Still another disadvantage of the lapping technique is the large number of three-angle cutting blades needed to machine different types of valve seats. Each type of engine has a different valve seat profile. Thus, one or more unique three-angle cutting blades may be needed for each type of engine.
In view of the aforementioned inadequacies of the prior art, the need exists for a cutting tool and a method to machine valve seats that substantially reduces flexions during machining and uses a universal cutting blade.
It is an advantage of the present invention to provide one universal cutting bit and bit holder having the ability to precisely machine an unlimited number of valve seat shapes.
It is an advantage of the present invention to substantially reduce flexion of the cutting bit during valve seat machining.
It is another advantage of the present invention to eliminate de-centering phenomena due to unbalanced radial efforts from flexion.
Yet another advantage of the present invention is to eliminate vibrations, chattering, and undulations to provide improved roundness in a valve seat.
In an exemplary embodiment, the present invention is a machining head comprising a fixed sleeve, a carriage head, a carriage head holder, a pinion feed driving assembly, and a universal cutting blade. The fixed pilot is attached to the bottom of the carriage head along the z-axis of a machine spindle. The carriage head holder attaches to the lower end of the machine spindle so that when the machine spindle is rotated, the machining head rotates. The carriage head is attached to the carriage head holder at an inclined angle relative to the bottom surface of the carriage head. The fixed sleeve is attached to a spindle sheath and provides cooperation with the pinion feed driving assembly to move the carriage head inward or outward when the machine spindle is rotated. The universal cutting blade is mounted on the carriage head through one of a plurality of mounting holes. The machining head can be utilized with virtually any conventional valve seat machining system, but is preferably used with the system disclosed in U.S. Pat. No. 5,725,335 of the present inventors.
The exemplary embodiment comprises a driving system, a machining head, a pilot, a depth gauge, and a system controller. The driving system further comprises a machining sphere, a machine spindle, a spindle sheath, a drive motor, a linkage, and a stepper motor. The spindle sheath is disposed within and supported by the machine sphere. The spindle sheath is fixed within the x- and y- axis, but can move along the z-axis by the stepper motor. The stepper motor is electrically connected and controlled by the system controller. The machine spindle is disposed within the spindle sheath and rotates around its z-axis through a drive motor and transmission linkage. The drive motor rotating the machine spindle is electrically connected to and controlled by the system controller.
The depth gauge is disposed on the spindle sheath by a fixed arm and is electrically connected to the system controller. The depth gauge measures the distance between a top surface of a cylinder head and the cutting blade.
The system controller includes a memory which contains software for controlling the operation of the cutting tool. This system controller includes a user interface at which an operator can input the parameters that define the geometry of a valve seat profile. These parameters are used by the system controller to determine the vertical feed rate of the machine spindle, the length of the vertical displacement of the spindle to machine the segment, and the number of rotations needed to machine a segment of the valve seat profile. The system controller uses a look-up table stored externally or within internal memory and the input information is used to determine the vertical feed rate of the machine spindle, the length of the vertical displacement of the spindle to machine the segment, and the number of rotations needed to machine a segment of the valve seat profile. The operator simply needs to center the spindle, activate the system after the initial input of information for a given cylinder head and valve seat profile, and re-center on each subsequent valve seat before activation.
The method for machining valve seats comprises four steps. First, a cylinder head is secured beneath the cutting tool and a valve seat is centered using the fixed pilot of the cutting tool. Second, the vertical feed rate of the machine spindle, the length of the vertical displacement of the spindle to machine the segment, and the number of rotations needed to machine a segment of the valve seat profile are calculated by the system controller from input parameters of the valve seat profile. Third, the system controller adjusts the vertical feed rate to cut each segment according to the desired valve seat profile and positions the cutting bit to an initial position. In one embodiment the initial position is a point radially farthest from the center of the valve seat. The rotation of the spindle moves the carriage head and cutting bit radially inward as the vertical feed rate is adjusted for each segment of the valve seat profile. Fourth, the system controller returns the cutting blade to its initial position through lifting the spindle and reversing the spindle rotation by the exact number of rotations used to machine the valve seat.